This application claims priority to co-pending United Kingdom Patent Application No. 9825891.6
The present invention is concerned with the detection and identification of pressure sensor faults within the context of electro-hydraulic (EHB) braking systems.
A typical EHB system for a vehicle comprises a brake pedal, respective braking devices connected to the vehicle wheels and which are capable of being brought into communication with electronically controlled proportional control valves in order to apply hydraulic fluid under pressure to the braking devices, a hydraulic pump driven by an electric motor, and a high pressure hydraulic pressure accumulator fed by said pump for the provision of hydraulic fluid under pressure which can be passed to the braking devices via the proportional control valves in order to apply hydraulic fluid under pressure to the braking devices in so called xe2x80x9cbrake by wirexe2x80x9d mode in proportion to the driver""s braking demand as sensed at the brake pedal.
The EHB system is controlled by an electronic controller (ECU) which, inter alia, controls the hydraulic pump to keep the pressure in the hydraulic pressure accumulator within specified limits.
The hydraulic pressure supplied to the electronically controlled valves (the xe2x80x9csupply pressurexe2x80x9d) is monitored by a supply pressure sensor. The hydraulic pressure at the various braking devices is measured by individual pressure sensors at these braking devices. An isolating valve is included whereby the hydraulic pressure accumulator can be selectively isolated from the pump and the remainder of the system.
Pressure sensors are key components of such EHB systems, being used in the process of controlling pressure as well as in the detection of system faults. Pressure sensors of the type in question convert hydraulic pressure into electrical signals which are supplied to the system""s ECU for control purposes. If one of these sensors develops a fault, such that incorrect signals are supplied to the ECU, then control errors could result. Incorrect pressure readings therefore have the potential to cause uncomfortable and/or inconsistent control of the normal braking function, to impair the efficiency of control systems such as ACC (Autonomous Cruise Control) or ABS, to trigger false warnings of system failure, or to overlook the occurrence of genuine system faults. For these reasons one wishes to detect even relatively small sensor errors so that effects such as the above can be mitigated by effective countermeasures.
Some types of fault can be detected by the sensor""s individual on-board electronics, but others are most easily (and economically) found by comparison with the signals of another sensor subjected to the same hydraulic pressure. Sensor duplication is, however, uneconomic.
It is therefore one object of the present invention to enable faults to be detected and identified by sensor signal comparison but without requiring sensor duplication.
In accordance with the present invention, three or more pressure sensors are arranged to be subjected to the same pressure and their readings measured and compared whereby to identify a sensor whose reading does not correspond to that of the others.
Preferably, in the case of a four or more wheeled vehicle, all pressure sensors associated with the braked wheels, and the supply pressure sensor, are connected together, with all of the proportional control valves opened fully or substantially fully.
In one test arrangement, with the vehicle stationary and the accumulator isolating valve open, a comparison of the readings from all sensors is made under pressure.
In an alternative test arrangement, the comparison of the sensor readings is made with the vehicle stationary and the accumulator isolating valve closed.